In the metal extrusion arts, it is well known to provide extrusion presses for the indirect extrusion of a metal billet through an extrusion die by the process of holding the axially-elongated billet within a billet container by means of a dummy block or closing plate. A powerful ram is employed to force the contained billet, together with the container, in the axial direction over an elongated hollow stem which carries an extrusion die at the free end thereof. The die thus passes axially into and through the container within which the metallic billet resides to extrude the billet through the die, thereby producing an extruded form. Such indirect extrusion operations result in the formation of a butt or waste portion of the billet at the end of the container adjacent to the closing plate, as it is not possible to extrude all of the billet through the die. The prior art has provided various ways and means for removing the butt end of the billet as is required to free the extruded form from the die and to permit repetitive use of the die. For example, U.S. Pat. No. 3,530,702 discloses an indirect extrusion press including a cutoff saw which is utilized to separate a major extent of the extruded form from a stud end portion thereof whereby the extrusion is separated from the butt end of the billet. U.S. Pat. No. 3,563,079 discloses an indirect extrusion press having a cutoff shear mounted on the forward platen thereof for shearing the billet butt end off of the die.
Other prior art approaches to butt end removal and die handling have included a cutoff shear carried on a longitudinally-movable carrier to move along the ways which also guide and support the main ram crosshead and the container housing, or a shear mounted on the container housing itself.
The prior art has been subject to certain shortcomings. For example, in those extrusion presses having a cutoff shear fixedly mounted adjacent to the platen, the stem which carries the extrusion die must be axially movable with respect to the platen through a considerable range of motion as in the cited U.S. Pat. No. 3,563,079. Such a movable stem is not necessary per se to indirect extrusion operations, but is provided only as an accommodation for the location of the cutoff shear. Accordingly, the press is more complicated in design and operation than it need be. Additionally, it will be noted that to utilize a shear mounted on the forward platen, the die and butt end of the billet must be forced back through the container at the conclusion of each extrusion operation requiring also a large shifting force. This results in considerable unnecessary wear on the interior walls of the container, as well as the possibility of metal coating tear up on the container walls, causing remaining metal particles to form blisters on subsequent extrusions. Also, to prevent the butt from tearing off the die face eliminating the possibility for the butt to become lodged in the container and especially when employing a loose die, the die and butt should be forced back through the container by means of a long stem, resulting in an unnecessary long press design and longer operating times. In those prior extrusion machines wherein a cutoff shear is mounted on the container housing, the reaction surface for the shear is the lower portion of the container interior periphery. Accordingly, large shear stresses are imposed on the container and container housing during butt shearing and the imposition of such forces may result in undue wear on the interior of the container and container housing, also causing misalignment of the container housing or carrier. To prevent shear force action on the container bore, other prior art introduced a cumbersome device supporting the die while shearing (outside the container) thereby transferring the shear load to the container housing.
Other prior art configurations, including the mounting of the cutoff shear on a separate carrier structure moving axially between the forward platen and the container require an un-necessarily long hollow die stem and are also unduly complex and therefore may adversely affect the tooling, duration operating efficiency and machine and tool cost.